FIGS. 1A through 1C show representative structures of optical add/drop multiplexers used in optical communications systems, such as WDM (Wavelength Division Multiplexing) and PXC (Photonic Cross Connect).
FIG. 1A shows a structural example of an F-OADM (Fixed Optical Add/Drop Multiplexer). The left side of FIG. 1A shows an internal structure of an optical add/drop multiplexer 1, and the right side of FIG. 1A shows a network structure using such multiple optical add/drop multiplexers 1. In the optical add/drop multiplexer 1, an N-channel multiplexed signal is amplified at an optical amplifying unit 11, and then the amplified signal is demultiplexed into individual channels at a demultiplexing unit (DMUX) 12. Subsequently, one or more of these demultiplexed channels are input to a multiplexing unit (MUX) 13 via a transponder 15 while the remaining channels are passed directly through to the multiplexing unit 13. The outputs of the demultiplexing unit 12 and the inputs of the multiplexing unit 13 are connected with patch cables. The multiplexing unit 13 multiplexes signals of N channels into one signal, which is amplified at an optical amplifying unit 14 and then output.
FIG. 1B shows a structural example of an R-OADM (Re-configurable Optical Add/Drop Multiplexer). In the optical add/drop multiplexer 1, an N-channel multiplexed signal is amplified at the optical amplifying unit 11, and then the amplified signal is demultiplexed into individual channels at the demultiplexing unit (DMUX) 12. Subsequently, each optical switching unit 16 corresponding to a different one of the N channels passes the corresponding channel through to an input of the multiplexing unit 13, or transmits it to the transponder 15. The optical switching units 16 are remotely controlled by software, and one or more channels go through the transponder 15. The multiplexing unit 13 multiplexes signals of N channels into one signal, which is amplified at the optical amplifying unit 14 and then output.
FIG. 1C shows a structural example of WSS (Wavelength Selective switch), which is a type of R-OADM. In the optical add/drop multiplexer 1, an N-channel multiplexed signal is amplified at the optical amplifying unit 11, and the amplified signal is passed through to a wavelength selective switch 17 capable of selectively switching signal transmission with respect to each wavelength. Subsequently, the signal is amplified at the optical amplifying unit 14 and then output. Also, the N-channel multiplexed signal output from the optical amplifying unit 11 is demultiplexed into individual channels at the demultiplexing unit 12. Subsequently, one or more of the demultiplexed channels are input to the multiplexing unit 13 via the transponder 15, and then input to the wavelength selective switch 17. This structure has an advantage of being able to establish a hub structure illustrated in the right side of FIG. 1C.
Optical communications systems such as WDM and PXC have been progressively developed to achieve higher capacities. Accordingly, optical cables used in optical add/drop multiplexers have been reduced in size and increased in density, and also the handling and operation of these multiplexers have become increasingly complex.
When optical cables are connected at the start-up of an optical add/drop multiplexer and at the time of maintenance, cleaning is a necessary and important task since dirty connectors have an adverse effect on communication quality, such as a reduction in the optical level, and disrupt the communications. Thus, before connection, dirt on connectors needs to be cleaned with a connector cleaner.
However, since the core diameter of optical connectors is 10 μm, the cleaning results cannot be judged by the naked eye, and in order to check the transmission condition of the connectors, the optical level needs to be measured by actually transmitting optical signals through the connectors. Particularly for high-density multicore optical connectors, cleaning and transmission checks are difficult to conduct.
FIG. 2 shows an example of a, conventional optical level checking technique. An optical add/drop multiplexer 1X of an X station and an optical add/drop multiplexer 1Y of a Y station are connected by two optical cables 2. The optical add/drop multiplexers 1X and 1Y are each based on the R-OADM technology illustrated in FIG. 1B. As for reference numerals assigned to components of the optical add/drop multiplexers 1X and 1Y, “(W)” is attached to the reference numerals of components located on the left side (West side when north is the top of FIG. 2) of the optical cables 2 while “(E)” is attached to those of components located on the right side (East side) of the optical cables 2.
According to FIG. 2, an operator of the X station connects a full-band laser measuring device 3X to optical switches SW of an optical switching unit SW(W) of the optical add/drop multiplexer 1, and also connects an optical spectrum analyzer 4X to an output monitor port of an optical amplifier Post-Amp of an optical amplifying unit AMP(W). The operator also connects an optical power measuring device 5X to optical couplers CPL of the optical switching unit SW(W). In the same manner, an operator of the Y station connects a full-band laser measuring device 3Y to optical switches SW of an optical switching unit SW(E) of the optical add/drop multiplexer 1Y, and also connects an optical spectrum analyzer 4Y to an output monitor port of an optical amplifier Post-Amp of an optical amplifying unit AMP(E). The operator also connects an optical power measuring device 5Y to optical couplers CPL of the optical switching unit SW(E).
Subsequently, as the operators of the X and Y stations communicate with each other with mobile phones or the like, a signal is transmitted between the two stations in end-to-end checking, and optical loss is measured for each path. If the condition measured for an optical path is less than a reference set point, the path is cleaned and then a measurement is made again. Specifically, at the X station, an optical signal having a wavelength corresponding to a target optical path is generated at the full-band laser measuring device 3X, and transmitted from an optical switch SW of the optical switching unit SW(W) of the optical add/drop multiplexer 1X. The optical power of the optical signal is measured by the optical spectrum analyzer 4X at the output monitor port of the optical amplifier Post-Amp of the optical amplifying unit AMP(W), and the optical power of the optical signal is also measured by the optical power measuring device 5Y connected to an optical coupler CPL of the optical switching unit SW(E) of the Y station. Herewith, it is possible to determine whether there is dirt on a multicore cable between the optical switching unit SW(W) and the wavelength multiplexing/demultiplexing unit MUX/DMUX(W) of the optical add/drop multiplexer 1X, and whether there is dirt on a multicore cable between the wavelength multiplexing/demultiplexing unit MUX/DMUX(E) and the optical switching unit SW(E) of the optical add/drop multiplexer 1Y. In the same manner, at the Y station, an optical signal having a wavelength corresponding to a target optical path is generated at the full-band laser measuring device 3Y, and transmitted from an optical switch SW of the optical switching unit SW(E) of the optical add/drop multiplexer 1Y. The optical power of the optical signal is measured by the optical spectrum analyzer 4Y at the output monitor port of the optical amplifier Post-Amp of the optical amplifying unit AMP(E), and the optical power is also measured by the optical power measuring device 5X connected to an optical coupler CPL of the optical switching unit SW(W) of the X station. Herewith, it is possible to determine whether there is dirt on a multicore cable between the optical switching unit SW(E) and the wavelength multiplexing/demultiplexing unit MUX/DMUX(E) of the optical add/drop multiplexer 1Y, and whether there is dirt on a multicore cable between the wavelength multiplexing/demultiplexing unit MUX/DMUX(W) and the optical switching unit SW(W) of the optical add/drop multiplexer 1X.
Japanese Laid-open Patent Application Publication No. 2005-26899
Japanese Laid-open Patent Application Publication No. 2002-223197
According to the conventional technique as described above, with respect to each wavelength, a corresponding optical signal is added while the operators on both ends are communicating with each other, and then the optical power of the added optical signal is measured end-to-end and is also measured, by the optical spectrum analyzer 4X/4Y, in the middle of the transmission path where the optical signal is multiplexed with other optical signals. Accordingly, the following problems are observed with the conventional technique.
(1) The measurements need to be made end-to-end between two individual devices (multiplexers) and thus cannot be made in a single closed device, whereby the checking process is burdensome.
(2) Since an optical signal having a predetermined wavelength is actually generated for the checking process, the measurements cannot be made for optical signals having wavelengths being used. Accordingly, the measurements can be carried out only at the initial start-up of the multiplexers, or the operation of the device needs to be stopped in order to conduct the measurements.
(3) It is sometimes the case that the transmission within a multiplexer is degraded with age or after replacement of a broken package having been in operation. In such a case, cleaning optical connectors is the only effective way to restore the transmission condition.
(4) In the case of a multiplexer using multicore optical connectors, even though only one core needs to be cleaned, the operation of other lines has to be stopped for the cleaning due to the configuration of the multicore optical connector, which results in imposing a considerable burden on the operators.
On the other hand, Patent Document 1 discloses an optical relay device capable of specifically determining a failure or a fault part within the device. Patent Document 2 discloses an optical network system capable of readily securing the quality of transmission according to the digital signal level.
However, the technologies of Patent Documents 1 and 2 monitor a failure or the transmission quality by the relationship with another device, and therefore, the measurements cannot be made in a single closed system. Thus, the above-mentioned problems cannot be solved by these disclosed technologies.